1. Field of the Invention
The present invention relates to a distance measuring equipment for measuring a distance up to a target to be measured in distance in such a manner that light is projected and light reflected on the target and returned is detected, and a camera incorporated thereinto such a distance measuring equipment.
2. Description of the Related Art
Hitherto, there is widely spread a camera incorporating thereinto an automatic focusing (AF) device, which is generally referred to as an active type. Such an active type of automatic focusing device adopts a system for measuring a distance up to a camera subject in such a manner that an AF light projection unit and an AF photo detection unit are disposed at intervals of a predetermined base length, light is projected from the AF light projection unit to the camera subject, and light reflected on the camera subject is detected by the AF photo detection unit. As a photo detector element for focusing, for example, a semiconductor photo detector, such as an SPD element and a PSD element, is used. By way of example, Japanese Patent Application Laid Open Gazette Sho. 57-22508 discloses a system in which a PSD element is used to perform a focusing.
To perform a photography using such a camera, first, a shutter button is subjected to a half-push operation. Then, light for focusing is projected from the AF light projection unit ahead of the camera, and light for focusing, which is reflected on the camera subject and returned, is detected on a detecting surface of a semiconductor photo detector so that a photo-current is generated. A distance up to the camera subject is determined in accordance with the generated photo-current, and a photographic lens is moved to the distance thus determined. In this manner, a focusing is performed by the AF device, and then the shutter button is subjected to a full-push operation to perform a photography.
Generally, as a distance up to the camera subject is far, a photo-current from the semiconductor photo detector is smaller. Thus, S/N ratio of a signal representative of a photo-current is lowered, and it is difficult to exactly determine the distance up to the camera subject. In view of the foregoing, Japanese Patent Application Laid Open Gazette Hei. 4-48208 discloses a technology of enhancing accuracy in focusing for both the short distance and the long distance, using a PSD element as the semiconductor photo detector, in such a manner that in case of the short distance there is adopted a focusing algorithm in which the ratio arithmetic value of photo-currents I1 and I2 outputted from the PSD element is integrated by a predetermined number of times so that a distance is calculated, and in case of the long distance there is adopted a focusing algorithm in which the addition value of photo-currents I1 and I2 outputted from the PSD element is integrated by a predetermined number of times so that a distance is calculated.
However, in the event that it is unclear as to whether a distance up to the camera subject is within an area of the short distance, it is a problem as to which one of the above-mentioned two algorithms is adopted to determine the distance.
According to the technology disclosed in Japanese Patent Application Laid Open Gazette Hei. 4-48208, arithmetic operations based on a plurality of focusing algorithms are simultaneously performed, and then it is decided as to which one of the operation results is adopted. In this case, the dedicated-arithmetic operation units are needed for the plurality of focusing algorithms, respectively. This is associated with a problem of increment of a circuit scale. Further, in this case, while the plurality of focusing algorithms are adopted, it is restricted to the use of plurality of focusing algorithms under such a condition that a photo sensor and a circuit unit directly relating to the photo sensing are in a certain fixed state. This is associated with a problem that a degree of freedom of selection of the focusing algorithms is low. For example, in the event that a detected signal derived by a photo sensor is amplified and transmitted to an arithmetic unit, there is a need to fix an amplification factor of an amplifier for amplifying the detected signal to a certain factor. Thus, it is impossible to adopt both the focusing algorithm wherein the amplification factor is set up to a lower factor and the focusing algorithm wherein the amplification factor is set up to a higher factor.
Alternatively, it is considered that an approximate distance, which is recognized by an operator of a camera through eye measurement, is taught to the camera. In this case, however, there is a need to provide an operation button and the like for performing such an operation, and the operation is troublesome per se. Further, it is considered that an operator forgets the operation and performs a photography. This is not preferable.
In view of the foregoing, it is an object of the present invention to provide a distance measuring equipment capable of performing efficiently a greater accuracy of focusing without troubling an operator, and a camera incorporating thereinto such a distance measuring equipment.
To achieve the above-mentioned object, the present invention provides a first distance measuring equipment for measuring a distance up to a target to be measured in distance in such a manner that light is projected and light reflected on the target and returned is detected,
wherein said distance measuring equipment has a plurality of focusing algorithms for measuring a distance up to the target to be measured in distance, any one of the plurality of focusing algorithms is used to perform a first focusing, and a number of times of focusing is determined in accordance with the first focusing.
According to the first distance measuring equipment, any one of the plurality of focusing algorithms is used to perform a first focusing, and a number of times of focusing is determined in accordance with the first focusing. This feature makes it possible to perform a focusing with greater accuracy without troubling an operator.
To achieve the above-mentioned object, the present invention provides a second distance measuring equipment for measuring a distance up to a target to be measured in distance in such a manner that light is projected and light reflected on the target and returned is detected,
wherein said distance measuring equipment has a plurality of focusing algorithms for measuring a distance up to the target to be measured in distance, any one of the plurality of focusing algorithms is used to perform a first focusing, and a focusing algorithm to be used for a second focusing and subsequent focusing is determined in accordance with the first focusing.
According to the second distance measuring equipment, any one of the plurality of focusing algorithms is used to perform a first focusing, and a focusing algorithm to be used for a second focusing and subsequent focusing is determined in accordance with the first focusing. This feature makes it possible to perform a focusing with greater accuracy without troubling an operator.
For example, the embodiments, which will be described later, relate to an embodiment in which both the embodiment of the first distance measuring equipment of the present invention and the embodiment of the second distance measuring equipment of the present invention are compounded. According to such an embodiment, a sort of the focusing algorithm and the number of times of focusing are determined in accordance with a distance to be measured in such a manner that in the first focusing the focusing algorithm according to the ratio arithmetic procedure is used to determine focusing data, and in the event that the focusing data thus determined is sufficiently reliable, that is, in the event that the focusing data is involved in the short distance area wherein a value of a noise component included in the photo signal for focusing is relatively small, the subsequent focusing is not carried out, and in the event that the focusing data is involved in the middle or so, that is, in the event that the focusing data is involved in the middle distance area wherein a value of a noise component is the middle or so, a focusing is performed a plurality of number of times in accordance with the focusing algorithm in the first focusing, and on the other hand, in the event that the focusing data is relatively low in reliability, that is, in the event that the focusing data is involved in the long distance area wherein the value of the noise component is relatively large, the focusing algorithm based on the light quantity is used to perform the focusing once.
Here, in the above-mentioned distance measuring equipment of the present invention, it is preferable that said distance measuring equipment has a semiconductor photo detector element comprising a detection surface for generating a photo-current upon receipt of irradiation of light, and a pair of signal electrodes, disposed at both ends of said detection surface, adapted for outputting on a share basis the photo-current generated by irradiation of light onto said detection surface in accordance with respective distances between an irradiation position on said detection surface and both ends of said detection surface, and
wherein said distance measuring equipment has, as said plurality of focusing algorithms, at least a focusing algorithm for computing a distance according to the irradiation position on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, and a focusing algorithm for computing a distance according to an irradiation intensity on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned.
Alternatively, in the above-mentioned distance measuring equipment of the present invention, it is preferable that said distance measuring equipment has a semiconductor photo detector element comprising a detection surface for generating a photo-current upon receipt of irradiation of light, and a pair of signal electrodes, disposed at both ends of said detection surface, adapted for outputting on a share basis the photo-current generated by irradiation of light onto said detection surface in accordance with respective distances between an irradiation position on said detection surface and both ends of said detection surface, and
wherein said distance measuring equipment has, as said plurality of focusing algorithms, at least a focusing algorithm for computing a distance in accordance with an arithmetic operation using as a variable both of a pair of photo-currents outputted from said pair of signal electrodes through irradiation on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, and a focusing algorithm for computing a distance in accordance with an arithmetic operation, using as a variable one of a pair of photo-currents outputted from said pair of signal electrodes through irradiation on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, between said variable and a selectable constant by which another photo-current is replaced.
Further alternatively, in the above-mentioned distance measuring equipment of the present invention, it is preferable that said distance measuring equipment has a semiconductor photo detector element comprising a detection surface for generating a photo-current upon receipt of irradiation of light, and a pair of signal electrodes, disposed at both ends of said detection surface, adapted for outputting on a share basis the photo-current generated by irradiation of light onto said detection surface in accordance with respective distances between an irradiation position on said detection surface and both ends of said detection surface, and
wherein said distance measuring equipment has, as said plurality of focusing algorithms, at least a focusing algorithm for computing a distance in accordance with an arithmetic operation using as a variable both of a pair of photo-currents outputted from said pair of signal electrodes through irradiation on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, a focusing algorithm for computing a distance in accordance with an arithmetic operation, using as a variable one of a pair of photo-currents outputted from said pair of signal electrodes through irradiation on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, between said variable and a selectable constant by which another photo-current is replaced, and a focusing algorithm for computing a distance according to an irradiation intensity on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned.
In the above-mentioned distance measuring equipment of the present invention, it is preferable that said distance measuring equipment has a semiconductor photo detector element comprising a detection surface for generating a photo-current upon receipt of irradiation of light, a pair of signal electrodes, disposed at both ends of said detection surface, adapted for outputting on a share basis the photo-current generated by irradiation of light onto said detection surface, and a first switch, disposed at a position adjacent to one signal electrode which is one of said pair of signal electrodes, for selectively offering a first state which permits the photo-current generated on said detection surface to conduct into said one signal electrode, and a second state which inhibits the photo-current generated on said detection surface from conducting into said one signal electrode, in accordance with a control signal; and
wherein said distance measuring equipment has, as said plurality of focusing algorithms, at least a focusing algorithm for computing a distance up to the target to be measured in distance in accordance with both photo-currents obtained from said pair of signal electrodes, in a state that said first switch offers the first state, and a focusing algorithm for computing a distance up to the target to be measured in distance in accordance with photo-current obtained from another signal electrode different from said one signal electrode of said pair of signal electrodes, in a state that said first switch offers the second state.
In this case, it is preferable that in said semiconductor photo detector element, when said first switch is in the first state, said pair of signal electrodes output on a share basis the photo-currents generated by irradiation of light onto said detection surface in accordance with respective distances between an irradiation position of the light on said detection surface and both the ends of the detection surface.
In the above-mentioned distance measuring equipment of the present invention, it is acceptable that said distance measuring equipment has a semiconductor photo detector element comprising a semiconductor photo detector element comprising a detection surface for generating a photo-current upon receipt of irradiation of light, signal electrodes, connected to associated divided areas of said detection surface, respectively, adapted for outputting the photo-current generated by irradiation of light onto said detection surface, and a second switch, disposed at a boundary between divided areas of said detection surface, for selectively offering a first state which permits the photo-current generated on said detection surface to conduct through the associated boundary, and a second state which inhibits the photo-current generated on said detection surface from conducting through the associated boundary, in accordance with a control signal; and
wherein said distance measuring equipment has, as said plurality of focusing algorithms, at least a focusing algorithm for determining a distance up to the subject in accordance with a plurality of photo-currents derived through said signal electrodes, in a state that said second switch is changed over to the second state, and a focusing algorithm for determining a distance up to the subject in accordance with the photo-current derived through a first signal electrode which is one of said signal electrodes, in a state that said second switch is changed over to the first state.
In this case, it is preferable that said semiconductor photo detector element comprise.s a third switch, provided in association with another signal electrode excepting said first signal electrode, for selectively offering a first state which permits the photo-current generated on said detection surface to conduct into the associated signal electrode, and a second state which inhibits the photo-current generated on said detection surface from conducting into the associated signal electrode, in accordance with a control signal,
one of said plurality of focusing algorithms determines a distance up to the subject in accordance with a plurality of photo-currents derived through said signal electrodes, in a state that said first switch is changed over to the second state, and said second switch is changed over to the first state, and
another of said plurality of focusing algorithms determines a distance up to the subject in accordance with the photo-current derived through said first signal electrode, in a state that said second switch is changed over to the first state, and said third switch is changed over to the second state.
Adoption of the semiconductor photo detector element having the above-mentioned switch makes it possible to implement a greater accuracy of distance measuring equipment with a smaller circuit scale and thereby reducing the cost of the device.
Here, while it is noted that said first state is a low impedance state, and said second state is a high impedance state, the state is not always restricted to magnitude of the impedance. A state which permits the photo-current to conduct through the switch is the first state, and a state which inhibits the photo-current from conducting into the switch is the second switch.
To achieve the above-mentioned object, the present invention provides a first camera having a distance measuring equipment for projecting light for focusing in front of the camera and detecting light reflected on a subject to determine a distance up to the subject, said distance measuring equipment moving a shooting lens to the determined distance,
wherein said distance measuring equipment has a plurality of focusing algorithms for measuring a distance up to the subject, any one of the plurality of focusing algorithms is used to perform a first focusing, and a number of times of focusing is determined in accordance with the first focusing.
In the above-mentioned first camera, it is acceptable that said camera performs a series of focusing to determine once a position of the shooting lens, and any one of the plurality of focusing algorithms is used to perform a first focusing of the series of focusing to determine once a position of the shooting lens, and a number of times of focusing up to completion of the series of focusing is determined in accordance with the first focusing.
To achieve the above-mentioned object, the present invention provides a second camera having a distance measuring equipment for projecting light for focusing in front of the camera and detecting light reflected on a subject to determine a distance up to the subject, said distance measuring equipment moving a shooting lens to the determined distance,
wherein said distance measuring equipment has a plurality of focusing algorithms for measuring a distance up to the subject, any one of the plurality of focusing algorithms is used to perform a first focusing, and a focusing algorithm to be used for a second focusing and subsequent focusing is determined in accordance with the first focusing.
In the above-mentioned second camera, it is acceptable that said camera performs a series of focusing to determine once a position of the shooting lens, and any one of the plurality of focusing algorithms is used to perform a first focusing of the series of focusing to determine once a position of the shooting lens, and a focusing algorithm to be used for a second focusing and subsequent focusing up to completion of the series of focusing is determined in accordance with the first focusing.
In each of the above-mentioned first and second cameras, it is preferable that said distance measuring equipment has a semiconductor photo detector element comprising a detection surface for generating a photo-current upon receipt of irradiation of light, and a pair of signal electrodes, disposed at both ends of said detection surface, adapted for outputting on a share basis the photo-current generated by irradiation of light onto said detection surface in accordance with respective distances between an irradiation position on said detection surface and both ends of said detection surface, and
wherein said distance measuring equipment has, as said plurality of focusing algorithms, at least a focusing algorithm for computing a distance according to the irradiation position on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, and a focusing algorithm for computing a distance according to an irradiation intensity on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned.
In each of the above-mentioned first and second cameras, alternatively, it is preferable that said distance measuring equipment has a semiconductor photo detector element comprising a detection surface for generating a photo-current upon receipt of irradiation of light, and a pair of signal electrodes, disposed at both ends of said detection surface, adapted for outputting on a share basis the photo-current generated by irradiation of light onto said detection surface in accordance with respective distances between an irradiation position on said detection surface and both ends of said detection surface, and
wherein said distance measuring equipment has, as said plurality of focusing algorithms, at least a focusing algorithm for computing a distance in accordance with an arithmetic operation using as a variable both of a pair of photo-currents outputted from said pair of signal electrodes through irradiation on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, and a focusing algorithm for computing a distance in accordance with an arithmetic operation, using as a variable one of a pair of photo-currents outputted from said pair of signal electrodes through irradiation on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, between said variable and a selectable constant by which another photo-current is replaced.
Further alternatively, it is preferable that said distance measuring equipment has a semiconductor photo detector element comprising a detection surface for generating a photo-current upon receipt of irradiation of light, and a pair of signal electrodes, disposed at both ends of said detection surface, adapted for outputting on a share basis the photo-current generated by irradiation of light onto said detection surface in accordance with respective distances between an irradiation position on said detection surface and both ends of said detection surface, and
wherein said distance measuring equipment has, as said plurality of focusing algorithms, at least a focusing algorithm for computing a distance in accordance with an arithmetic operation using as a variable both of a pair of photo-currents outputted from said pair of signal electrodes through irradiation on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, a focusing algorithm for computing a distance in accordance with an arithmetic operation, using as a variable one of a pair of photo-currents outputted from said pair of signal electrodes through irradiation on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned, between said variable and a selectable constant by which another photo-current is replaced, and a focusing algorithm for computing a distance according to an irradiation intensity on said detection surface of said semiconductor photo detector element, of the light for focusing reflected on the target and returned.
It is noted that cameras provided with various types of distance measuring equipment as mentioned above are included in a camera of the present invention.